Individual behaviour plays an important role in sustainable transport, however, daily mobility habits are difficult to change. Collaborating with formal social groups such as sports clubs appears to be an effective strategy to motivate participation in behaviour change programmes, but there is a lack in empirical work that systematically compares targeting groups and targeting individuals in such efforts. This paper reports on a quasi-experiment in the field offering this comparison. It was implemented in a programme of a Swiss city motivating sportspeople to attend sports training sessions by bike instead of by car. The programme addressed sports teams (n=187) and individuals exercising at gyms (n=31). Surveying modes of transport before, during, directly after, and a few months following the programme revealed that team members significantly reduced car use to training sessions during the programme. Social norms impacted team members' decisions to travel by car less frequently. In contrast, individual participants' car use to attend gym sessions was not affected by the programme. We conclude that formal social groups such as sports clubs are potentially effective multipliers and motivators for environment-friendly mobility programmes. More research is needed on how behavioural changes during the programme translate into long-term habitual changes.